Miniature axisymmetric supersonic nozzles were produced with exit Mach
numbers ranging from 1.0 to 2.8 by forming Pyrex(R) capillary tubing
of 0.6 and 1.2 mm inside diameter into converging-diverging channels.
The nozzle contours were measured and were found to compare favorably
to ideal solutions given by the axisymmetric method of characteristics
. In addition, the surfaces of these nozzles were quite smooth, provid
ing featureless flows at perfect expansion. Schlieren visualization an
d pitot pressure measurements of the resulting microjets were compared
to the literature available for jets produced by larger-scale nozzles
. A postponed transition to turbulence is noted in these microjets due
to their low Reynolds number. The pitot pressure on centerline is nea
rly uniform at perfect expansion over core lengths up to 12 nozzle exi
t diameters. Supersonic microjet nozzles thus provide a more effective
small-scale high-pressure gas delivery device than do sonic nozzles o
f comparable scale at equivalent mass flow rates. Supersonic microjets
may therefore have several industrial applications.